Diagnostic Procedures for Allergy

Nasal smears. Nasal smears are tests performed to check the amount of eosinophils in the nose. Eosinophils are a type of white blood cell that increases in number during an allergic reaction.

Blood tests. Blood tests for allergies measure IgE (immunoglobin E) antibodies to specific allergens in the blood. The blood test most commonly used is called RAST (Radio Allergo Sorbent Test). Blood tests may be used when skin tests cannot be performed. As with skin testing, it is important to remember that a positive blood test does not always mean you are allergic to that allergen.

Challenge test. A test supervised by an allergist who administers a very small amount of an allergen that is inhaled or taken orally.

Skin tests. The skin test is a very accurate test that measures your level of IgE antibodies in response to certain allergens or triggers. Using small amounts of solution that contain different allergens, the doctor will either inject under the skin or apply the allergens with a small scratch. A reaction would appear as a small red area. A reaction to the skin test does not always mean you are allergic to the allergen that caused the reaction. This will be determined by your doctor.

Skin testing is usually not performed on children who have had a severe life-threatening reaction to an allergen or have severe dry skin (eczema).